It is conventional to form components which are partially or totally of plastic, particularly large components such as vehicle door panels and the like, in a reaction injection mold press (commonly referred to as a "rim" press) with the part being formed in a mold cavity defined between relatively movable upper and lower mold parts. For forming a component such as a vehicle door panel, various techniques can be utilized. For example, a vinyl sheet which can be heated and vacuumed formed, and possibly in conjunction with a fiberglass sheet, can be positioned in the mold cavity and polyurethane deposited into the cavity to permit molding of the desired component within the press. In some circumstances the vinyl is premolded or preshaped, or in other circumstances the molded component is formed without a vinyl layer.
The conventional mold presses for forming such components are often mounted on a turntable which indexes through a plurality of stations formed along a circular work path. While this arrangement does provide convenience with respect to efficient movement of multiple presses into and through spaced workstations, nevertheless such turntable arrangement typically permits access to the press and specifically to the upper and lower mold parts only from one side, and this greatly hinders and restricts the desired access to the press since workers must access the press so as to not only insert whatever premold parts and components are necessary, but also to assist in removal of the molded part.
As an alternative, many of the known mold presses are freestanding units. This increases worker access by typically permitting access to the press at least from opposite sides thereof. Nevertheless, the overall molding process associated with a single press involves several stages and hence requires significant time, and thus efficient use of workers accordingly normally requires that the workers move back and forth so as to permit servicing of several adjacent freestanding presses. Such arrangement is less efficient than desired, and more fatiguing for workers.
With the known mold presses, as briefly discussed above, the opening and closing movement of the press, as well as the press closure force, is typically controlled by fluid pressure cylinders, normally hydraulic cylinders. Such press arrangements, however, are generally energy inefficient since the use of hydraulic cylinders as the energizing source, and the overall support equipment necessary to provide and supply pressurized hydraulic fluid to the press cylinders, results in significant energy loss in relationship to the electrical energy which is supplied so as to effect operation of the press fluid system. In addition, presses employing hydraulic cylinders for creating the moving and pressing function of the press have also demonstrated an undesirable noise level associated with the fluid cylinder system. Such systems also typically experience leakage of hydraulic fluid, which can create an undesired and sometimes potentially hazardous condition around the press. The hydraulic systems also generate significant and often undesired heat.
Accordingly, it is an object of this invention to provide an improved mold press which is believed to overcome many of the disadvantages and inconveniences associated with known mold presses, as briefly summarized above, and which is believed to provide for improved efficiency of operation, improved energy efficiency, and improved convenience of access and use.
More specifically, the improved mold press of this invention includes a drive arrangement for controlling the press movement and closure force which is totally electric so as to eliminate the use of hydraulic cylinders and the like, whereby the overall energy efficiency of the press is significantly improved, and at the same time, heat generation and oil leakage problems associated with conventional hydraulic cylinder presses are eliminated. The improved mold press and specifically the drive arrangement includes a pair of generally identical drive units which are associated with and connected between the upper and lower press plates adjacent opposite longitudinal ends of the press. The drive units in a preferred embodiment each employ a screw-nut drive arrangement, preferably a ball-screw arrangement. The screw shaft is an elongate member which extends vertically between the top and bottom press plates, with the screw shaft engaging a ball nut assembly which is mounted on one of the press plates, typically the bottom press plate which is disposed for movement toward and away from the top press plate. A first high speed drive arrangement employing a first electric motor is coupled to the screw shafts for effecting high speed rotation and hence effecting high speed opening and closing movement of the bottom press plate. A second low-speed driving arrangement including a second electric motor is drivingly connected to the ball-nut assemblies of the two drive units for permitting a low-speed but high-torque driving of the nut units for final closing of the press and application of the desired press force. Each drive unit preferably has the screw shaft resiliently supported for limited axial displacement relative to the upper press plate so that, when the second drive system is activated to effect final closure of the mold one or the other of the screw shafts can be axially displaced a small amount if necessary so as to permit full closure between the opposed upper and lower mold parts even though irregularities may cause one longitudinal end of the mold parts to contact and close prior to the other longitudinal end.
In the improved mold press of this invention, as aforesaid, the first and second drive systems are typically separately actuated in that only the first drive system is activated so as to permit high speed movement of the lower press plate during closure of the lower mold part toward the upper mold part until substantially reaching the closed position. At such time the first drive system is deactivated, and preferably a locking device is actuated which then engages and holds the screw shaft nonrotatable. The second drive system is then activated to effect rotation of the ball nut assemblies associated with the lower press plate to effect final closure of the mold and imposition of the desired mold pressure between the upper and lower mold parts. During activation of the second drive system, if one end of the mold parts contact and close prior to the other end, then the nut assembly associated with said one end continues to drive, and the associated screw shaft is axially displaced in opposition to the resilient structure associated therewith until the drive unit associated with the other end of the mold parts senses proper closure, at which time the second drive system is de-energized. The screw mechanisms associated with the drive units then effectively maintain the mold parts in a closed or locked position whereby imposition of further driving force is not required, even though the mold parts remain in their closed and effectively locked position.
In accordance with the present invention, as aforesaid, the mold press is preferably mounted on a self-propelled overhead carrier associated with and driven along an overhead rail system so that the mold press is suspended from the carrier and free of direct support from the underlying floor. The overall system preferably includes a plurality of carriers each mounting thereon a mold press, with the carriers being sequentially moved through a plurality of spaced stations along the overhead track, the latter preferably defining a loop, to facilitate efficient use of the presses by permitting various functions to be carried out at spaced workstations, with the presses being efficiently transferred between workstations, and with the actual molding operation being carried out either as the carrier is transferred between workstations or is shuttled into an intermediate holding zone for sufficient duration to permit the desired molding of the component. With the mold press mounted on a driven overhead carrier, the press provides greatly increased access to the mold parts by workers, and for example both the upper and lower mold parts can be mounted on respective upper and lower press plates which vertically swing into more convenient access positions, with the upper mold part swinging into a position accessible from one side of the press, and the lower mold part swinging into a position accessible from the opposite side of the press, whereby two workers located on opposite sides of the press can readily and simultaneously access the respective upper and lower mold parts to facilitate preparation of the mold. Other access positions or arrangements can also be provided.
In addition, the improved mold press of this invention includes a electric drive arrangement for controlling the opening and closing movement between upper and lower press plates. The drive arrangement includes a pair of generally parallel ball-screw drive units which extend vertically and cooperate with the movable press plate for controlling opening and closing movement thereof. The press is mounted on a self-propelled overhead carrier associated with and driven along an overhead rail system so that the press can be sequentially moved between the plurality of working stations. The ball-screw drive units are driven from an electric motor which is mounted on and moves with the carrier, with electrical power being supplied to the carrier in a conventional fashion from an electrical supply track which extends along the overhead rail system.
Other objects and purposes of the invention will be apparent to persons familiar with assemblies of this general type upon reading the following specification and inspecting the accompanying drawings.